The instant invention relates to environmental control in general, and specifically to the prevention of smog through the reduction of objectionable constituents which would otherwise be discharged into the atmosphere. The latter are often found in varying degrees in the exhaust fumes of internal combustion and diesel engines.
It is known that by recirculating all or a part of the exhaust created by an engine, the amount of pollutants which enter the atmosphere can be reduced. To foster this concept regulations have been imposed which are becoming more stringent. Their objective is to minimize the amount of pollutants which will be discharged into the atmosphere regardless of the engine's running status.
This gas recirculation is normally achieved by extracting at least a part of the exhaust gas stream and reintroducing it at some point where it will mix with the initial charge entering the engine's respective combustion chambers.
One problem inherent with the extraction of the exhaust stream for recirculation, is that different engines operate, exhibiting different firing characteristics in the combustion chambers. It has been found generally, however, that the major part of the undesirable pollutants, such as hydrocarbons are discharged during the exhaust stroke, at the beginning of the stroke and at the end thereof. Thus, to recirculate a part of the exhaust gas stream for reburning with the initial charge, it has been found that the overall charge introduced to the cylinder's inlet valves lacks uniformity and can vary widely in quality.
Because of the desire to control the combustion event in any cylinder, and thereby to a degree to control the quality of the exhaust gas, it has become desirable to regulate more closely the composition of the overall charge. That is, in the instance of a premixed charge, the air and fuel, as well as the exhaust gas, are combined to form the aggregate charge. To have the engine work efficiently and satisfactorily from the point of view of emissions control, it is desirable to maintain a degree of uniformity and consistency in this initial aggregate charge.
It has been determined as noted, that a major portion of the undesirable constituents which make up any exhaust charge, are discharged from the cylinder during particular periods of the exhaust stroke. In one example it was found that approximately 40% of the hydrocarbons were discharged from the cylinder in the first 5.degree. to 10.degree. of travel of the exhaust stroke. Of the remaining charge, 50% of these constituents were discharged during the last 10.degree. to 15.degree. of travel.
It has been determined therefore that an acceptable amount of undesirable constituents entering the atmosphere can be tolerated and controlled. The present system thereby provides a means for intermixing the exhaust gas which is drawn from each of a plurality of cylinders in the engine. Further the segment of said exhaust gas is extracted during the final part of the engine stroke.
The system includes means to sequentially introduce a sufficient portion of the exhaust charge from each cylinder into a common chamber. Thereafter, from this chamber the exhaust gas is metered, and fed to the intake manifold or to the air filter. Thus, said aggregate exhaust gas can be readily mixed with incoming charge whether the latter be premixed, stratified, or otherwise.
It is therefore an object of the invention to provide a system for minimizing the amount of undesirable gaseous constituents which are passed to the atmosphere from an internal combustion engine. A further object is to operate said engine within predetermined standards which are designed to hold down the amount of possible air pollutant constituents which might otherwise be discharged into the atmosphere. A still further object is to provide means to assure a degree of uniformity in the makeup of a charge which enters the intake of the engine's cylinders during any and all operating periods.
The objectives of the invention are achieved through means of an exhaust gas mixer which is commonly communicated with the respective engine cylinders. During each cylinder's exhaust stroke, the final portion of the hot gas is introduced to a mixing chamber rather than into the engine's exhaust manifold. Within the mixing chamber, gases from each of the cylinders are readily intermixed and subsequently passed to the intake manifold or to the air inlet for mixing with the charge.